I'd read that it's mainly the upper frequencies that are affected, but I had an experience yesterday that made me question that.
 
The night before, lying in bed with my best headphones on I listened to a mix and made a mental note that there wasn't enough bass in the mix. Next morning as soon as I awoke and before getting out of bed I grabbed the cans and listened to it again. My early-morning evaluation was "what was I thinking last night? There's plenty of bass."
 
There is one other variable that deserves mention, and that is the presence of tetrahydrocannabinol during the previous night's audition. There is no doubt that marijuana affects sensory perception, but I would have assumed its effect would be a heightening of sensitivity. This experience suggests the opposite may be true.
 
But considering how many classic records had marijuana as an ingredient, could it be that deadening frequency perception might be a good thing? Does it perhaps lead you to make more dramatic mix decisions such as gobs of bass or super-compressed drums? The first guy to stick a $1000 microphone an inch from a drum had to have been smokin' something.

Bristol_Jonesey
I'm guessing not your thumb..................

Actually, you are correct? It was not my thumb. However, the thumb is not actually considered a finger? It is "the opposable thumb..." It allows us to do what we do musically? Therefore, there are 4 guesses.
 

bitflipper
 The first guy to stick a $1000 microphone an inch from a drum had to have been smokin' something.

or just a $600 Beyer M160 ribbon on a snare....  which is probably the 2nd most popular mic used for that, back when...  Probably threw a TV set out the window, that same day.

bitflipper
I'd read that it's mainly the upper frequencies that are affected, but I had an experience yesterday that made me question that.
 
The night before, lying in bed with my best headphones on I listened to a mix and made a mental note that there wasn't enough bass in the mix. Next morning as soon as I awoke and before getting out of bed I grabbed the cans and listened to it again. My early-morning evaluation was "what was I thinking last night? There's plenty of bass."
 
There is one other variable that deserves mention, and that is the presence of tetrahydrocannabinol during the previous night's audition. There is no doubt that marijuana affects sensory perception, but I would have assumed its effect would be a heightening of sensitivity. This experience suggests the opposite may be true.
 
But considering how many classic records had marijuana as an ingredient, could it be that deadening frequency perception might be a good thing? Does it perhaps lead you to make more dramatic mix decisions such as gobs of bass or super-compressed drums? The first guy to stick a $1000 microphone an inch from a drum had to have been smokin' something.

I was under the impression that it was the musos taking the bong hits, not the engineer. The musicians playing the choons on weed, the engineer straight as a die wondering how in the hell he was going to make this crap sound good, and the manager coked up to the eyeballs demanding more cow bells. 

Sidroe
Your hearing can change in a matter of seconds depending on how you subject your ears to db and air pressure levels. Do a google on ear fatigue. I learned what little I know from a high school bud that went on to med school and is a practicing ear doctor. Based on what he told me I drastically reduced my levels and TIME spent under headphones! I just turned 62 two weeks ago. I have been suffering from tinnitus going on about 30 to 35 years. I attribute it to standing in front of a Marshall Super Lead 100 watt stack all those years in clubs and on the road.
I have set guidelines now in my studio work producing that I never track and mix on the same day. Mixing at high levels never lasts more than a couple of hours at most. Headphones may be used for tracking, never mastering. If it still isn't right, I try again the next day. No deadline is worth your hearing!
I, too, have lived in apartments where you had no choice but headphones. Just try to be very judicious volume and time wise underneath those things. I don't know what your age is but I can tell you, I sure would have taken better care of my hearing back then. I am paying for it now.

I too have tinnitus, had it since my 20's. Am not sure exactly when it started, I think it just crept up on me but I was too stoned to notice. In my case it was a combination of being in thrash bands when I was younger, then dancing high as a kite to acid trance music for 12 hours straight in front of huge speakers at illegal raves for much of the early 90's. Oh and a few Metallica/Slayer/Dio gigs in the late 80's. Not to mention the long hours spent listening to Frank Zappa on headphones. Considering all of that though, I think my hearing has fared pretty well. I can't hear much over 15-16k but that's common for my age (41). 
 
I use headphones a lot (both at home and in the gym) but I try to keep the volume reasonable and I always stop at regular intervals and have a 10 minute break. One thing I've been doing for the past year, and I'm sure many will think I'm mad, but I've been taking a good magnesium supplement (i.e. not oxide) a couple of times a day. This was after reading from multiple sources that it can protect the ears from noise damage. Well before doing any work on headphones in the evening, I'll take a couple of chelated magnesium pills ("Doctor's Best" brand) and drink some Natural Calm, a magnesium drink which also really helps me relax in the evenings and melts away the tension. It's not a substitute for avoiding loud noise, but I figure that as part of a regime of noise caution it can only help. I've also heard that resveratrol is touted as a protection against hearing loss, so it'll be interesting to see how those studies go.
 
New York is one hell of a noisy city. I'm out and about on the streets of Manhattan most days and you're constantly bombarded with sirens, construction noise and of course the deafening subways. I always stick my fingers in my ears when a train goes past, especially when they're applying those horrible squeaky brakes. Looking around I see that hardly anyone else does it, which is a shame considering how many times New Yorkers have been told how potentially damaging subway noise is. God knows what it's doing to kids.  

sharke
I was under the impression that it was the musos taking the bong hits, not the engineer. 

You haven't read The Daily Adventures of Mixerman.

440 pages..that looks like quite a read. I could go for something funny.